1. Field of the Invention
The present invention concerns the technical sector of vehicles provided with tires and on-board safety systems concerning them. “Vehicles” will, throughout the present application, including the claims, mean both light vehicles (LVs), such as private cars or vehicles, and utility vehicles or heavy vehicles such as lorries and “heavy goods vehicles” (HGVs), their trailers, forestry vehicles, civil engineering machinery, military or emergency vehicles, and the like.
2. Description of the Related Art
The general technical problem which is posed is that of accidental pressure loss (APL) which can go as far as leading to running flat, with vehicles equipped with tires. The phenomenon of APL and, ultimately, running flat designates, as a person skilled in the art knows, the running of the vehicle on at least one tire whose inflation pressure becomes or has become, for any reason whatsoever, very much less than the pressure provided for by the manufacturer, that is to say the case of running where the inflation pressure drops abnormally with respect to the nominal operating pressure, referred to as the service pressure, the inflation pressure even being able to become zero.
The causes of these phenomena are very numerous: running over a perforating object, impact on a shape of the “pothole” type or the edge of a pavement, deterioration of the valve, damage to the rim (dented rim with loss of seal at the seat), etc, and are well known.
Amongst the devices for combating these problems of serious loss of pressure and running flat and their consequences there figure in particular devices for sealing the puncture and tires with the ability to run flat on a support.
The devices for sealing the puncture are based on so-called “sealing products” whose function is to block the hole giving rise to the perforation of the tire. In order to be effective, these sealing products must be sufficiently adherent to the internal surface of the tire and to the object responsible for the puncture, if this object remains locked in the tire. They must also be capable of withstanding the inflation pressures and the forces sustained in running. Such products are usually relatively viscous.
The patent U.S. Pat. No. 5,295,525 presents such a sealing product intended to be disposed, during the manufacture of the tire for example, on the surface of the internal cavity thereof. These products can be effective for holes of limited size, but this efficacy decreases rapidly over time and the presence of these products in the tires greatly complicates their mounting and removal. Consequently the presence in a tire of such sealing coatings does not completely eliminate the risk of a user having to stop in the event of a puncture.
The patent U.S. Pat. No. 5,648,406 presents a sealing product intended to be introduced into the internal cavity of a tire only after a puncture. The sealing product is then usually contained in an aerosol can and is introduced into the internal cavity through the inflation valve and applied against the internal surface of the tire by virtue of the action of a compressed gas present in the aerosol can. In general, these aerosol cans are used by the user. They have the advantage of being less expensive, less heavy and less bulky than a spare wheel, but require the stoppage of the vehicle, which represents an extremely serious drawback for the user. In addition, these anti-puncture aerosol cans are not effective in all cases, in particular in certain cases of rapid puncture that is to say in the case where a large perforation has occurred.
More recently, tires with the ability to run flat have appeared on the motor vehicle market. The majority of these tires are equipped with a pressure measurer intended to inform the user that one or more of his tires have suffered or are suffering an APL. The majority of these devices also measure the temperature of the internal air so as to correct the value of the pressure from the variations in value of the temperature, according to the law of perfect gases.
Some of these tires or mounted assemblies, that is to say tire and rim assembly, comprise a “support” disposed around the rim, in the internal cavity of the tire. Amongst this type of mounted assembly with the ability to run flat, the PAX System can be cited. Such a support consists for example of a vulcanized rubber material which can be reinforced by textile or metallic cable reinforcements.
In the event of abnormally low pressure, the interior of the tire crown comes into contact with this support. In doing this, the support limits the flexing of the tire flat and makes it possible to continue running under given conditions of maximum speed and distance.
However, during such running flat, the contacts between the internal wall of the tire crown and the external wall of the support take place with significant relative sliding between these two walls. This relative sliding is due to the fact that the distance traveled in one turn of the wheel by the tire crown is greater than that traveled by the exterior of the support with which it is in contact. A difference in running radius is spoken of. In order to limit the friction forces due to these relative slidings and their consequences in terms of heating and mechanical damage, it is possible to use a lubricant inside the internal cavity of the tire. This lubricant will reduce the coefficient of friction between the interior of the tire crown and the exterior of the support and enable the two bodies to slide with respect to each other whilst limiting the mechanical damage and heating. The lubricant can be disposed on the surface of the support when the mounted assembly is manufactured and/or assembled, and can also be placed in adapted receptacles in order to be opened only in the event of need (see U.S. Pat. No. 4,054,168, by way of example).
The performance of this lubricant is important for the flat running to take place correctly. In many cases, as the quantity of lubricant disposed inside the internal cavity of the tire is necessarily limited, if it were possible to increase the quantity of lubricant, the range of the mounted assembly in running flat would be increased. It should also be noted that the presence of this lubricant can complicate any work involved in mounting and removing the mounted assembly.
The document WO 02/04237 presents a lubricant composition which can be used for lubricating an interface between a tire and a safety support. This lubricating composition comprises essentially on the one hand a lubricating agent including glycerin and on the other hand a polysaccharide intended to thicken this lubricating agent.
Centralized inflation devices called “CTIS” (Central Tire Inflation System) have been appearing on the market for several decades. These devices enable the driver of a vehicle to modify the inflation pressure of the tires on his vehicle according in particular to the adhesion conditions encountered (see U.S. Pat. No. 5,516,379 by way of example).
These devices have the advantage of allowing periodic checking of the inflation pressure of the tires on the vehicle and thus to supplement the quantity of air contained in one of the tires when there is a slight leak for example.